This invention relates to aluminosilicates, more particularly to amorphous sodium aluminosilicates of especial use in detergent compositions.
It has been known for many years that aluminosilicates are useful in removing hardness ions from aqueous systems and, more recently, a large number of patent specifications have been published concerning various crystalline and amorphous aluminosilicate-containing detergent compositions. In these compositions the aluminosilicate is intended to replace, in part or in whole, the phosphate compositions which have hitherto been used.
The zeolites, or crystalline aluminosilicates, have long been known and are relatively stable materials which readily remove calcium ions from aqueous systems. The preferred type "A" zeolites do not, however, have a very significant effect on magnesium ions and it has previously been noted that amorphous aluminosilicates have the benefit of removing both calcium and magnesium ions from aqueous systems.
However, known amorphous aluminosilicates have one significant defect, namely that they react with sodium silicate, which is an important constituent of most detergent compositions. The mechanism of the reaction between amorphous aluminosilicate and sodium silicate is not fully understood, but its effect is to lessen the effectiveness of the aluminosilicate as a detergent builder in that it slows down the removal of hardness ions and may also reduce the capacity of the aluminosilicate for such ions.
Efforts have been made to overcome this deficiency in amorphous aluminosilicates by modifying the production process of detergent compositions containing these two materials. For example, British Patent Specification No. 2 013 707 suggests an alternative route for manufacturing detergent compositions in which the sodium silicate is added to the detergent composition in such a way as to minimise the reaction between the sodium silicate and the sodium aluminosilicate.